Lens surfacing techniques



19, 1959 c. H. LA FRANCE 2,886,923

. LENS SURFAGING TECHNIQUES Filed Jan. 18, 1957 H I v ]NVENTOBS GYR/LLE.II. LA FRANCE ATTO EY United Statcs Patent O LENS SURFACNG TECHNIQUESCyfille H. La France, Southbrdge, Mass., assignort American OpticalCompany, Southbridge, Mass., a voluntary association of MassachusettsApplication January 18, 1957, Serial No. 634,990

Claims. (Cl. 51-185) This invention relates to improvements in abradingapparatus and has particular referenceto the provision of an improvedlens abrading tool and method of making the same.

In general, prescriptive curvatures are applied to ophthahnic lensblanks by rough grinding or generafing the approximate desired curvatureon a particular side thereof, fine grinding said side to the precisecurvature desired and thereafter polishing the fine ground side to ahigh degree of optical perfection. The fine grinding or fining operationis most commonly accomplished by placing the surface of the lens blankin contact With a cast iron surfacing tool having et surface curvaturethereon which is precisely formed to the desired curvature to bereproduced upon said lens blank and thereafter applying a slurrycontaining abrasive particles of a selected size to said tool surfacewhile introducing a controlled pressure and oscillatory motion to eitheror both the tool and lens blank so as to cause the abrasive particles toabrade the surface of the blank and thus cause said surface toeventually assume the shape of the surface of the tool. Unfortunately,however, the abrasive action of the slurry, during such an operation,causes a detrimental wearing away of the preformed surface of the toolwhich, after continued use, eventually introduces errors of curvature tosaid tool surface and, consequently, to the surfaces of the lens blanksgenerated thereby. For this reason, it has been necessary to carefullygauge the curvature of the abrading surface of the tool before eachfining operation and, When an excessive amount of wear has taken place,the abrading surface is renewed by a commonly known time-consuming andcostly conventional tool truing operation. It has been found that theaverage tool must be trued after each 3 or 4 grindingoperaflons andeventually this requires replacement of the tool.

Another disadvantage of such tools in the past, in order :to aid inavoiding the forming of socalled burned spots on the generated surface,has been the necessity,

when truing a tool surface, to groove or recess portions of said surfacein an attempt to produce a more even distribution of theabrasivc slurryduring the abrading operation. Such grooving or recessing is also timeconsuming and costly.

The present invention, therefore, is intended to over-- corne theabovementioned difficulties and other limitations inherent inpresent-day lens surfacing techniques through the provision of novelmeans and method for :surfacing lenses or the like wherein the abradingsurface of a tool of the above-mentioned type is provided with a readilyreplaceable facing which, when applied to said tool, will accuratelyassume the preformed shape of and become the effective abrading face ofthe tool.

Another object of the invention is to provide inexpensive detachable anddisposable grinding face portions for a lens surfacing tool of thecharacter described which may 'be simply and rapidly attached to orremoved from the tool and which will protect and preserve the preformedsurface thereof dun'ng the abrading operations and there- Patented May19, 1959 by eliminate the heretof0re age-old expansive and time-'consuming tool truing operations.

Another object is to provide an inexpensive disposable tool facing offoraminous material which may be quickly and simply shaped and attachedto a prefonned curved surface of a conventional lens grinding tool.

Another object is to provide a protective disposahle wire mesh facingfor a lens grinding tool of the above A further object is to providenovel means and metliod of eliminating the requirement of human judgmentin gauging lens grinding tools and the necessity of having an expensivesurface truing machine as has heretofore been essential and to therebypermit a precision factor} control of the curvatures of the grindingtools used in said grinding operations.

A still further object is to provide removable grinding facings for lensgrinding tools of the above character which facings are of approximatelythe same thickness as that of the conventional polishing pads normallysubsequentl applied to the curved surfaces of said tools for polishingpurposes, whereupon replacement of a grinding facing with a conventionalpolishing pad will produce substantially no change in the desired radiusof curvature of the working face of the tool.

Other objects and advantages of the invention will Fig. is a fragmentarysectional view sirnilarto Fig. 4 1llustrang an alternative type offacing and attachmerit means embodying the invention;

Fig. 6 is a side elevational view of a further modified" form ofgrinding tool embodying the invention; and

Fig. 7 is a diagrammatic fragmentary side view of a lens surfacingapparatus illustrafing a particular use for a grinding tool of the typeembodying the invention.

Referring more particularly to the drawings in which like referencecharacters represent like parts throughoirt tl1e several views thereof,the device embodying the inven-- trou comprises a lens surfacing tool 10having a body por tion 11 formed of cast iron or any other suitableshape' retaining material having a curved surface 12 on one side thereofshaped substantially to the curvature desiredto be formed on one side ofa lens blank and a wire mesh facing 13 detachably secured thereto.

In such an arrangement, the exposed surface of the facing 13 becomes theabrading surface of the composite surfacing tool 10. This, of course,difiers from the conventional surfacing tool in that it has beenthepractice heretofore to perform the lens abrading operations directlyupon the curved preformedsurface 12 of the tool which unavoidably causesa wearing away of said surface and, after continued use, introduceserrors of curvature and other deformities in the resultant finishedsurfaces of the lens blanks being abraded thereby.

It is particularly pointed out that although the im -mediate descriptionis directed principafly to a Wir'e mesh"- type of facing, it isconceivable that other readily conformable types of foraminous facingmaterials may be used whiIe being Well Within the scope of the presentinvention.

In an attempt to avoid the well-known time-consuming and costly surfacetruing operations common to the trade, sheetlike replaceable coveringsor facings of metallic foil or the like have been used to protect theabrading surface of the tools. In practice, however, the use of suchcoverings has met With little or no success since it has been found thatthey are not readily conformable to the various degrees of curvaturerequired in the trade, particularly when constructed of a thicknessand/or durabitv sufiicient to withstand at least one abrading operation.In this case, the problem of conformabity has, of course, led to theproduction of inferior lens surfaces caused primarily by folds, creasesor stretched areas in the foil covering, which unavoidably occur Whileattempting to fit the foil to the abrading tool.

With this in mind, it is pointed out that the wire mesh facing 13 of thepresent invention may be of any desired thickness or durability sincethe interwoven condition of the strands 14 thereof is such as to permitsaid strands 14 to shift laterally relative to each other in such amanner as to allow the overall facing 13 to precisely assume the shapeof the surface 12 to which it is applied.

A soft steel galvanized wire mesh of 30 x 30 strands par inch with awire size of approximacely .007 inch has proven, for all practicalpurposes, to produce the most satisfactory results both from astandpoint of durability and conformability. However, other combinationsof wire sizes, mesh structures or types of wire such as bronze, nickel,etc. may be used.

Since the wear, normally incurred upon the abrading surface of theconventiorral cast iron surfacing tool, will, in the case of the presentinvention, take place upon the abrading surface of the wire mesh facing13, it is essential that said facing be of a readily replaceable anddisposable type which may be simply, etficiently and quickly attached toor removed from the surface 12 of tool 10. In this respect, theabovementioned steel galvanized mesh has proven to be of a durabilitysufiicient to out live the wearing effect of at least one lens surfacingoperaton while accurately producing the resultant surface of a lensblank being abraded thereon. Although a single wire mesh may berepetitively used without introducing any great distortion to theresultant lens surfaces being formed, it has been found that in order tomaintain a high standard of precision in said resultant lens surfaces,it is most practical to replace the mesh facing after each surfacingoperation.

With regard to the matter of attaching the facing 13 to the surface 12of tool l0, it is pointed out that this may be accomplished in many waysother than those shown or described herein. Nevertheless, the presentinvention is directed principally to a few novel and highly effectivetypes of attachment means. Figs. 3 and 4 best illustrate one preferredform in which the wire mesh 13, being initially in sheetlike form issprayed or otherwise provided on one side thereof With a suitable,relatively thin layer of any one of many commercially available slowsetting water proof adhesives, and immedialy thereafter flocked With asynthetic or natural fibrous material 15 such as, for example rayon,cotton or the like. The fibrous material is preferahly selected to be inlengths of %(5 of an inch or shorter. The flocking of the mesh may beaccomplished by blowing or otherwise applying the fibrous matefial tothe abovementioned adhesive treated mesh before the said adhesive hasset and simultaneously cloctrostatically, or otherwise causing the majorportion of each of the fibers of the flocking to stand away from theadhesive. Upon subsequent setting, the adhesive then bonds a part ofeach of the fibers of the flocking 15 securely to the wire mesh andprovides an overall plush coating which may be readily attached to thesurface 12 of1a tool 10-by spraying or otherwise applying a secondadhesive coating 16 to either the surface 12 or the flocking 15 andpressing the wire mesh against the surface 12. In pressing the wire mesh13 against surface 12, said mesh 13 will automatically accurately assumethe preformed shape of said surface 12 due to the relatively loose wovenconstruction thereof, as described above. It is pointed out that thismethod of attachment allows the flocked wire mesh, when in largesheet-Iike form, to be out to the approximate contour shape of thesurface of the tool, Figs. 1 and 2, prior to being attached thereto.doing, a saving in the wire material is accomplished since nooverlapping of the sides of the body portion 11 ofthe tool is necessary.

Another method of attaching the wire mesh 13 to tool 10 is shown in Fig.5 Wherein one side of the mesh 13 is suitably coated With a heatsensitive type of adhesive 17 such as for example, a composition of 75%rosin and 25% hydrogenated methyl ester of rosin or other adhesivehaving similar characteristics, which is adapted to fill in and aroundthe woven strands 14 of the mesh 13 and provide an all-over coatingwhich is securely bonded to the mesh and which would then be directlyapplied to the surface 12 of tool 19 by heating the tool 10 an amountsufiicient to cause said adhesive to soften and form a bond between thesurface 12 and mesh 13. Alternatively, any known pressure-sensitive typeof adhesive may be used in place of adhesive 17.

In either case, the mesh 13 having the adhesive mate-- rial 17 thereonenables the mesh to be out to size and stocked for future use. The useof a pressure-sensitive adhesive eliminates the necessity of having toclean the surfaces 12 of tools 10 after each removal of the. wire mesh13 since said adhesive normafly tends to be more positively bonded tothe interwoven strands 14 of the mesh and separates more cleanly fromthe smoother Surface 12 of the tool. The above-mentioned adhesives, ofcourse, in the cases of both Figs. 4 and 5 are of a type which willsecurely retain the mesh 13 in operative position of use whilepermitting said mesh to be easily and simply stripped from the toolfollowing the lens surfacing operations. The surfaces 12 may however, becleaned With a suitable adhesive solvant prior to each application of anew wire mesh facing if desired.

A further alternative in applying the wire mesh 13 to tool 10 is tosimply cut the mesh 13 largeenougb to overlap the sides of the bodyportion 11 of tool 10, as shown in Fig. 6 and to securely attach saidmesh to the tool 10 by means of a springtype clamp 18 or any othersuitable clamping means. 'Ihis method obviously requires the use of alarger piece of mesh 13 than the above-mentioned methods but, on theother hand, does not require the use of adhesives.

It is particularly pointed out that although the curved surfaces 12 ofthe surfacing tools 10 are illustrated as being convex, the wire meshfacings 13 may be made to conform to and be applied to concave toolsurfaces.

Referring more particularly to Fig. 7 the tool 10 is generally securedto a tool-supporting arm 19 or the like of a lens sunEacing machine by aclamp 19a, such as diagrammatically illustrated, and a lens blank 20having been previousiy properly adhesively attached to a holder 20a, ispositioned upon the wire mesh facing 13 of the tool 10. An oscillatingmotion is then usually imparted to the arm 19 while the attached lensblank 20, through suitable alignment retaining means 21 and crankspindle 22, simultaneously describes a path of movement relative to thatof the tool 10. The combined movements between the lens blank 20 andmesh 13 then produces a scrubbing action on the surface of the blank andan abrasive slurry 23 embodying particles of selected size is applied tothe mesh 13 so as to lie between said mesh and blank and due to thescrubbing action, abrade said sur-face of the blank t0 a point where itwill assume precisely the shape of the abrading face By so of the wiremesh 13. It is pointedout that the wear due to the abrasive action takesplace at the outer face of the wire strands 14.

An important featur'e of the present invention is that the interwovencondition of the wire mesh 13 permits the abrasive slmry 23 to flow inbetween and around the strauds 14 of said mesh 13 in such a manner as tomore evenly distribute said slurry to all parts of the surface of thelens blank being abraded. Ibis, of course, eliminates the so-calledundesired burned spots on the loris blanks which occasionally occur whena con ventionai smooth surface cast iron tool is used. Burned spts arecaused by an improper distribution of the abrasive particles between theengaging surfaces of the lens blank and tool and the resultant breakingclown of said particles which efiectively causes the lens surface beingabraded to be in direct contact with the tool surface.

To more fully understand another important feature of the presentinvention, namely that of providing factorycontrolled surface curvatureson abrading tools of the above-character, it is pointed out thatheretofore it has been the practice to repeatedly use the conventionalcast iron smooth surface tool until the abrading surface thereof hasbeen distorted by wear -to a point where, in accordance With thejudgment of an operator, the surface is so Worn as to produce inferiorlenses. Human errors of judgment in such cases are, of course, verycommon since many factors must be considered. For example, a greateramount of tool wear can be tolerated for the production of weak curveson lens blanks than in the case of the stronger curves. Sighting betweena curve sauge and tool surface, being checked for wear, demands greatskill and judgment on the part of the operator in determiuing the futureusefulness of the tool.

By providing a factorycontrolled surface curvature 12 on the bodyportion 11 of an abrading tool 10 of the type embodying this inventionand providing disposable and replaceable wire mesh facings 13 of theabove-described character to protect said factory-controlled surface 12,the abovementioned errors of human judgment are eliminated. In addition,and equa1ly as important particularly from an economical standpoint, thecostly and timeconsuming commonly known tool surface truing operationscan be completely abolished, since the surfaces 12 of the tool 10 arenever subjected to wear or abrasion.

With the present invention, the surface 12 of tool 10 would be providedat the factory with curvatures of radii s controlled as to compensatefor the thickness of the wire mesh facing 13 to be subsequenfly appliedthereto whereby the radii of curvatures at the abrading surface of thefacing 13, when applied to the tool, would be precisely that of theresultant surface desired on the lens blank. 'Dhe body portions 11 ofthe abrading tools would then be either molded directly to the desiredshapes through the use of sintered metals or plastics or tooled in theusual manner at the factory.

Subsequent to an abrading operation, it has been the practice heretoforeto attach a polishing pad to the abrading surface of the conventionalsurfacing tool and to finish the previously abraded lens blank surfaceby a polishing operation which is conducted in a manner similar to thatof the abrading operation with the exception of applying a polishingmedium to the tool and lens blank rather than an abrasive slurry. Insuch cases, however, when the face of the tool was directly used inabrading and was provided With the true curve to be reproduced on theblank the thickness of the polishing pad in many instances caused anoticeable change in the resultant radius of curvature of the polishedsurface formed thereby and also errors of curvature, due to wear of theabrading surface of the tool, which were brought about by the previousabrading operations and were also introduced during said polishingoperation.

The present invention avoids the abovementioned culties and permits theuse of more recenfly introduced superior types of plastic polishing padsthroughout the various ranges of curvatures known to the trade since thewire mesh abrading facing 13 can be controlled to be of a thicknesssubstantially equal to that of a polishing pad which would subsequentlyreplace said facing 13 during a polishing operation. Moreover, no errorsin curvature due to wear during a prev ious abrading operation canpossibly exist since such wear would be incurred only upon thedisposable wire mesh facing 13.

From the foregoing description, it is apparent that all the objects andadvantages of the invention have been accomplished to provide novelmeans and method for surfacing lenses.

It will also be apparent that many changes may be made in the details ofconstruction and arrangement of parts shovvn and described withoutdeparting from the spirit of the invention as expressed in theaccompanying claims. Therefore, it is to be understood that all materialset forth or shown in the accompanying drawings is to be interpreted asillustrative and not in a limiting sense.

Having described my invention I claim:

l. A replaceahle facing for a lens surfacing tool comprising a sheetingof interwoven metallic wire strands contoured to overlie and tointimately engage the effective surface of said lens surfacing tool andmeans for retaining said sheeting of interwoven metallic wire strands onsaid lens surfacing tool.

2. A protective abrading facing for a lens surfacing tool comprising aforaminous sheeting contoured to overlie at least the abrading sidesurface of a lens surfacing tool to be used therewith, said sheetingembodying a plurality of closely related interwoven metallic wirestrands, said strands being adapted to shift laterally with respect toeach other whereby said sheeting will accurately assume the particularshape of said side surface of the tool when forced thereagainst and thussubstantially reproduce said particular shape at its exposed surface,attachment means bonded to a side of said sheeting topermit saidsheeting to be detachably secured to said abrading side surface of thetool when properly fitted in a position of use thereon.

3. An abrading facing for a lens surfacing tool embodying a sheeting ofinterwoven metallic wire strands, said sheeting being contoured t0overlie at least the abradiug side surface of a lens surfacing tool tobe used therewith, the interwoven condition of said wire strands beingsuch as to permit relative lateral movement thereof whereby saidsheeting will readily conform to the particular shape of said abradingside surface of said tool when forced thereagainst and attachment meansfor detachably securing said sheeting to said lens surfacing toolembodying an adhesive-type bonding material between said sheeting andsaid abrading side surface of the tool.

4. An abrading facing for a lens surfacing tool embodying a sheeting ofinterwoven metallic wire strands, said sheeting being contoured tooverlie at least the abrading, side surface of a lens surfacing tool tobe used therewith, the interwoven condition of said wire strands beingsuch as to permit relative latera1 movement thereof whereby saidsheeting will readily conform to the particular shape of said abradingside surface of said tool when forced thereagainst and attachment meansfor detachably securing said sheeting to said lens surfacing tool, saidattachment means embodying a flock material bonded to one side of saidsheeting to form a plushlike surface thereon and an adhesive for bondingsaid plushlike surface to said abrading side surface of the tool.

5. A foraminous abrading facing for a lens surfacing tool embodying asheeting of interwoven wire strands, said sheeting being contoured tocover the abrading side surface of a lens abrading tool and additionallyoverlap a part of the edge portions of said tool, the interwovencondition of said wire strands being such as to permit.

relative lateral movement thereof whereby said sheeting Will rcadilyconform to the particular shape of said ab1fading side surface of saidtool When forced there against and attachment means for detachablysecuring said sheeting to said lens surfacing tool embodying a removableclamp member adapted to be placed in gripping surrounding relation withthe edge portions of said sheeting when said sheeting is in position ofuse on said tool.

6. A lens surfacing tool comprising a body portion having one sideshaped t fit within a supporting part of asurfacing machine With whichsaid tool is to be used and its opposed side provided With et surfacecurvature substantially in conformity With the curvature desired of. asurface of a lens to be formed by said tool and a foraminous facingoverlying and detachably secured to said opposed side of the tool inintimate fitted relation with the surface curvature thereof.

7. A lens surfacing tool comprising a body portion having one sideshaped to fit within a supporting part of a surfacing machine with-whichsaid tool is to be used and its opposed side provided With a surfacecurvature substantially in conformity With the curvature desired of asurface of a lens to be formed by said tool, a wire mesh facingoverlying and detachably secured to said opposed side of the tool inintimate fitted relation With the surface curvature thereof, said facingembodying a plurality of interwoven wire strands adapted to shiftlaterally With respect to each other t0 cause the overall facing toconform to the surface curvature of said opposed side of the tool whenforced thereagainst whereby said facing when in position of use on saidsurfacing tool Will provide an exposed abrading surface thereon inconformity with the curvatureof the surface of the tool to which it isapplied and the texture of said exposed abrading surface resulting. fromthe interwoven condition of said wire strands being such as to permit auniform distribution of an abrasive medium between said abrading surfaceand a lens blankin engagement therewith during the surfacing operation.

8. The method of making a lens surfacing tool comprising providing arigid supporting member having one side shaped substantially to thecurvature desired to be formed upon a lens blank, fitting a wire mesh.facing in intimate engaging relation with said shaped side of thesupporting member and detachably securi ng said facing;

in said fitted relation on said supporting member.

9. The method of making a lens surfacing tool comprising providing arigid supporting member having a side thereof shaped substantially tothe curvature desired to be formed upon a lens blank, providing aninterwoven facing or stranded wire parts contoured t0 O,Verlie at leastsaid shaped side of the supporting member, forcing said sectional sizeloosely interwoven so as to have interstices between the strands andthroughout the area of said sheet ing, said sheeting, because of theloosely interwoven strands which are readily shiftable relative to eachoth e r,

being adjustahle to relatively intimately fit the surface,

curva'ture of the tool While rtaining the interstices for permitting theflow and pocketing of the abrasive slurry normally applied to such toolsduring the use thereof, and means for replaceably securing said sheetingto said tool.

References Cited in the file of this patent UNITED STATES PATENTS Re.17,576 Maynard Jan. 28, 1930 369,431 Brown Sept. 6,1887- 1,166,639 HillJan. 4, 1916 2,024,303 Obrig Dec. 17, 1935 2,544,950 Ritterbusch et al.Mar. 13, 1951

